Variable resistor construction



L. M. BURGESS VARIABLE RESISTOR CONSTRUCTION Aug. 12, 1952 2 SHEETS-SHEET l.

Filed Oct. l1, 1950 Aug. l2, 1952 l.. M. BURGESS VARIABLE RESISTOR CONSTRUCTION 2 SHEETS-SHEET 2 Filed Oct. ll, 1950 Patented Aug. 12, 1952 VARIABLE RESISTOR CONSTRUCTION Lauren M. Burgess, Lexington, Mass., assigner to Technology Instrument Corporation, Acton,

Mass.

Application October 11, 1950, SerialNo. 189,661

7 Claims.

The present invention relates to a variable resistor construction of a type more commonly referred to as a precision potentiometer.

Certain circuit applications require tapped variable resistors or voltage dividers, more commonly called potentiometers, which are built with fixed taps. The precision construction required makes such devices relatively expensive. Not infrequently the calculations arrived at on the basis of certain assumptions for circuits are found to be inaccurate because of certain unanticipated circuit variables. To have the correct values in a tapped variable resistor or potentiometer then requires a change in the location of the tap, which can be accomplished only by Winding a new resistor element. Here again the inconvenience and cost is a distinct disadvantage. It, therefore, would be desirable to provide an improved variable resistor construction, which would obviate some of the disadvantages encountered by the commonly accepted practice.

Therefore, it is an object of the present invention to provide an improved variable resistor construction whereby a tapped potentiometer may be obtained having adjustable taps.

Still another object of the present invention is to provide an improved variable resistor construction, which will provide for a plurality of adjustable taps arranged to remain xed after initial adjustment.

Other and further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawing, wherein:

Figure 1 is a rear view of a precision variable resistor or potentiometer constructed in accordance with the present invention;

Figure 2 is a similar rear view of the device shown in Figure 1 with the rotary contact arm and slip ring removed;

Figure 3 is a cross-sectional view of the device shown in Figure 2 as seen in the direction of the arrows along the line 3--3 thereof;

Figure 4 is a rear view of a precision variable resistor or potentiometer showing another embodiment of the present invention;

Figure 5 is a cross-sectional View of Figure 4 as seen in the direction of the arrows along the line 5-5 thereof; and

Figure 6 is an enlarged detail view of one of the elements shown in Figures 4 and 5.

Referring to the drawing there isl shown a precision variable resistor, commonly known as a potentiometer, having a cylindrical housing I I. The housing I I has an end wall provided with an integrally formed bearing support I2 for re ceiving a suitable bearing sleeve. The bearing sleeve supports a rotary shaft I3 shown in Figure l having about its end a split sleeve I4. A rotatable arm I5 is mounted on the shaft I3 and held in position thereon by means of a suitable fastening screw passing through the bifurcated clamping ends I6, which compress the split sleeve I4 about the shaft I3.

Suitably supported from the end wall of the casing II is a metallic slip ring I 1, which is connected by a conductor I8 to a terminal I9 supported by an insulated terminal block 26. The slip ring I'I is engaged by a pair of contact brushes 2l, which are electrically connected to the movable contact arm 22, the outer end of which engages the resistor element 23. The resistor element 23 consists of wire wound on a suitable strip of insulating material, which is positioned in insulated manner adjacent the inner wall of the cylindrical housing I I. One end of the resistance element 23 is connected to an electrical terminal 24 mounted in the terminal block 20. The construction thus far described is conventional in variable resistors or potentiometers of the high precisions type.

An adjustably positioned tap 25 is arranged to engage the resistor element 23 at a selected point thereon. The adjustable tap 25 is connected by an electrical conductor 26 to a binding post or terminal 2l mounted in the terminal block 20. The adjustable tap 25 carries a precious alloy contact 2'8 for engaging a selected wire or wries of the resistance element 23. The adjustable contact 25 is held in position by a screw 29, which engages an insulated ring 3l. The insulated ring 3I is retained in position by a screw 32, the head of which engages the ring and the body of which passes into an annular boss 33. The annular boss 33 may have a tapered edge 34 adjacent the ring 3I.

The ring 3I may be moved about the annular boss 33 to any desired position thereby to move the contact 25 to engage a selected point on the resistance element 23. If subsequent to this adjustment it is fount that a finer adjustment of a turn or a portion of a turn is required for the contact, this can be accomplished by loosening the screw 29 and moving the contact 26 so that the precious metal tip 28 engages the desired turn of Wire on the resistance element 23. Thereupon tighteningr of the screw 29 will re tain in position the tip on the resistance element. It, of course, will be appreciated that While a single tap has been shown in the drawing for purposes of clarity, a plurality of such taps may be provided on the ring 3i Thus by adjusting the positions of the various taps by means of the ring 3|, a further renement in the position of any particular tap can be accomplished by the adjustment of that tap by means of its fastening screw 29. Variable resistors or potentiometers of this type are used in precision controlled circuits requiring a high degree of accuracy in winding the element 23 and in providing a tap or taps thereon. It, therefore, will be apparent to thoseskilled in the art that the present construction obviates certain of the disadvantages heretofore encountered in the use of tapped precision potentiometers.

In Figures Il, 5 and 6 another embodiment of the invention is illustrated. In this case the housing li is somewhat similar to the housing shown in the previous embodiment, but the back wall (l2 which carries a bearing sleeve 3E has a smaller annular boss Mounted about the annular boss it is a split ring de which normally has an inner diameter slightly less than the outer diameter of the boss dii. Thus when the ring engages the boss Zi-ii, a gripping action is obtained which securely holds the ring L35 in adjusted position. The ring i5 carries one or more electrical contacts de, each held in adjusted position on the ring t5 by a screw il?. The electrical contact 46 is provided with a precious metal alloy tip 48 arranged to engage selected wires on the wire wound resistance element 139.

The housing il is provided with a terninal block having electrical terminals 5l, 52 and 53. The terminal 5| is connected to one end of the resistance element i9 whereas the terminal 53 is connected to the slip ring, which is engaged by the movable contact arm corresponding to the arm l5 and its contact 22 shown in Figure l. Each of the adjustable contacts 135 s connected to a terminal, such as the terminal 52, by means of a suitable conductor.

If it is desired to move the Contact it to a selected position, a screw driver may be inserted between the ends of the split ring d5 so that it is spread somewhat as shown in exaggerated manner by the dotted line representation in Figure G. Thereupon the ring may be rotated about the boss d to position the contact ei. Thereafter the screw d? may be loosened and the precious tip 1S moved to the exact turn on the resistance element 5,9. lThis, of course, is of a distinct advantage where the ring l5 carries a plurality of contacts corresponding to the contact fit.

While for the purposes of illustrating and describing the present invention a certain preferred embodiment has been shown in the drawing, it is understood that the invention is not to be limited thereby, since all variations are contemplated which may be commensurate with the spirit and scope of the invention set forth in the accompanying claims.

I claim as my invention:

1. A variable resistor comprising a cylindrical housing having an end wall, a resistor element mounted within said housing about the inner cylindrical wall, a movable Contact carried by a rotary shaft, a bearing for said shaft in said end wall, an adjustable ring carrying a contact for engaging said resistor element, a support for said ring concentric to said bearing, and a lock screw for holding said ring and said latter contact in adjusted position.

2. In a variable resistor having a cylindrical housing provided with an end wall, a resistor element mounted adjacent the inner cylindrical wall, a movable contact for said element carried by a rotary shaft, a bearing for said shaft formed in said end wall, the combination comprising an adjustable ring carrying a precious metal alloy contact for engaging said resistor element, a support integral with said end wall for said ring concentric to said bearing, and a lock screw for holding said ring and said latter contact in adjusted position.

3. In a variable resistor having a cylindrical housing with an end wall carrying a bearing, a resistor element mounted adjacent the inner cylindrical wall, a rotary shaft mounted in said bearing, a movable contact for said resistor element carried by said shaft, the combination comprising a circular support formed as an integral part of said end wall, an adjustable ring mounted on said support, fastening means interconnecting said ring and said support for holding said ring in fixed adjusted position, and at least one precious metal contact mounted on said ring for engagement with a selected point on said resister element.

4.. In a variable resistor having a resistor element mounted on the inner cylindrical wall of a cylindrical housing, said housing having an end wall carrying a bearing for a rotary shaft, a movable contact mounted on said rotary shaft for engaging said resistor, a terminal block carried by said housing, the combination comprising a circular support formed as an integral part of said end wall, an adjustable insulated ring mounted on said support, fastening means interconnecting said ring and said support for holding said ring in adjusted position, at least one precious metal conta-ct mounted on said ring for engagement with a selected point on said resistor element, and a conductor interconnecting said precious metal Contact and said terminal block.

5. in a variable resistor having a cylindrical housing provided with an end wall, a resistor mounted within said housing, a rotatable contact for engaging said resistor, the combination comprising a circular support formed as an integral part of said end wall, an adjustable ring vmounted on said support, fastening means for locking said ring in adjusted position on said support, and means for adjustably mounting on said ring at least one precious metal contact for engagement with a selected point on said resistor element.

G. A variable resistor having a cylindrical housing with an end wall provided with a circular support formed integrally therein, a resistor element mounted adjacent the inner cylindrical wall, a rotary shaft carrying an arm having a contact for said resistor element, an adjustable split ring mounted on said support, said ring having an inner diameter slightly less than the outer diameter of said support, and at least one metal contact adjustably mounted on said ring for engagement with a selected point on said resistor element.

7. A tapped variable resistor comprising a cylindrical housing having an end wall, a bearing mounted in said wall, a rotary shaft mounted in said bearing, a resistor element mounted adjacent the .inner cylindrical surface of said hous- 5 6 ing, a movable contact mounted on said rotary REFERENCES CITED Shaft and engaging Said resistor element' an in' The foliowing references are of record in the sulated ring located concentric to said shaft and me of this patent: carrying an adjustably positioned contact for engagement with a selected point on said resistor 5 UNITED STATES PATENTS element, support means formed in the end wall Number Name Date of said housing concentric to said bearing for 1,669,687 Adams et a1. May 15, 1928 rigidly supporting said ring in a selected position, 1,881,446 Flanzer Oct. 11, 1932 and an electrical connection between said ad- 2,480,995 Armitage Sept. 6, 1949 justably positioned Contact of said ring and the 10 exterior of said housing.

LAUREN M. BURGESS. 

